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Hamiltonian math

by DiracPool
Tags: hamiltonian, math
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Dec9-12, 12:09 AM
P: 606
I'm watching a lecture on the Hamiltonian and can't figure out something. Here it is. Take a generic function G, and differentiate it with respect to p and q. What you get is the partial of G with respect to p TIMES the derivative of p (or p-dot), plus the derivative of G with respect to q TIMES q-dot.

My question is, where does the p-dot and q-dot terms come into the equation here? Why isn't it just the partial of G over p plus the partial of G over q?
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Dec9-12, 12:30 AM
jtbell's Avatar
P: 11,862
What you've described looks like taking the derivative of G(p,q) with respect to t, using the chain rule:

$$\frac{dG(p,q)}{dt} = \frac{\partial G}{\partial p} \frac{dp}{dt} + \frac{\partial G}{\partial q} \frac{dq}{dt}$$
Dec9-12, 12:52 AM
P: 606
It certainly does, thanks jtbell.

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